Temperature indicating apparatus



p 4, 1951 A. CHRISTENSON ET AL TEMPERATURE INDICATING APPARATUS SAWTOOTHWAVE Filed March 7, 1946 GENERATOR 1' R E FT LR C M PERIODIC SIGNAL IGENERATOR TO AMPLIFIER N 5N c m mmw mLT T 0AA NTc D INR E A N mM 'm 5 Hw W u W Rm UR WA Rm T A R Y C B D N A m mm Kc MD m 0 T. H

Patented Sept. 4, 1951 TEMPERATURE INDICATIN G APPARATUS Arthur L.Christenson, Alexandria, Va., and Clarence E. Jackson, Niagara Falls, N.Y.

Original application October 11, 1944, Serial No. 558,234. Divided andthis application March '1, 1946, Serial No. 652,745

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3700. G. 757) 3 Claims.

Our invention relates to electrical temperature indicating apparatus andmore specifically to a direct reading electronic apparatus whereinthermal lag produced by inertia of moving parts of instruments has beensubstantially eliminated.

This application is a division of our copending application SerialNumber 558,234 filed October 11, 1944, now Patent No. 2,478,895 andinsofar as it contains new matter it may be considered acontinuation-in-part thereof.

It is acknowledged generally in the art of pyrometry that evenmoderately precise measurement of extremely rapid changes in temperatureis extremely difiicult to perform in the study of transformations inmetals, for example, and other materials which are exposed to suddentemperature variations.

It is an object of our invention to provide an apparatus which hassuificiently speedy response and high enough sensitivity to measureaccurately the temperature changes in materials during rapid heating andcooling.

It is another object of our invention to provide an apparatus with whichthe temperature change in materials accompanying transformationsoccurring during a heating or cooling cycle can be followed.

It is a third object of our invention to provide an apparatus with whichtime rate of temperature change of a specimen being heated or cooled atany rate can be visually indicated and recorded.

A fourth object of our invention is to provide an apparatus in which theindicating device is substantially inertialess, thus making theapparatus extremely sensitive and responsive to the changes beingmeasured.

Other objects and advantages of our invention will in part be obviousand in part appear hereinafter.

Our invention comprises a temperature detecting and measuring device anda method and means for increasing the sensitivity thereof and includesthe combination of elements and relationship of parts and thecombinations of steps and the relationship to eachother which will bemore fully described hereinafter.

In describing our invention, reference will be made to the appendeddrawings in which:

Figure 1 is a general diagram of the apparatus, partially schematic;

Figure 2 is a representation of one form of thermoelectric detectingcircuit;

Figure 3 is a schematic representation of a second form ofthermoelectric detecting circuit;

Figure 4 is a diagram of a third form of thermoelectric detectingcircuit.

The device shown in Figure 1 comprises a thermocouple Ill which, uponbeing heated, produces a direct voltage proportional to the degree ofheating. This direct voltage is converted into a pulsating signal bymeans of a make-break device, schematically represented by contacts It.The pulsating signal produced thereby is amplified by the wide-band, twostage amplifier cir cult comprising tubes l2 and I3, the amplifiedsignal then being rectified by tubes I4 and I5, filtered byresistance-capacitance circuits [6 and I1 and applied to the deflectionplates of the cathode ray tube l8. A meanswhereby the sensitivity of thetemperature indication may be improved is provided by the thermocouplebiasing circuit comprising, a biasing cell IS, a resistor 20 and anadjustable resistor 2|. A sawtooth generator may be applied to theopposite deflection plates of the cathode ray tube to provide a timereference for the temperature measurements.

The principle of our invention can best be explained and understood byreferring to Figure 1. The temperature of a specimen is detected by athermocouple Ill attached to the surface of the specimen, saidtemperature producing a proportional voltage in the thermocouple.

Inasmuch as the maximum voltage output of common thermocouples isapproximately fifty millivolts (0,050 volt), it is desirable to amplifythe thermoelectric signal obtained in order to provide for convenientmeasurement. Because of the drift which would be encountered by using aresistance coupled amplifier as a means for amplifying such smallvoltages to a value necessary to give convenient deflection on a cathoderay tube screen, temperature calibration might easily be in error. Itis, therefore, advisable to employ a resistance-capacitance coupledamplifier, and since this type will amplify only alternating orpulsating currents, provision is made for deriving an alternating orpulsating signal from the thermoelectric voltage.

In the circuit diagram of Figure 1, the method of deriving the pulsatingsignal is indicated schematically by means of a pair of contacts I i.This make-break arrangement may take any one of several forms, as willbe indicated with reference to Figures 2, 3 and 4. The pulsatingtemperature signal obtained by the making and breaking of contacts I Ipreferably has a relatively high repetition frequency, i. e., about 500pulses per second. However, this is not a critical point, for we haveused pulse repetition frequencies as low as per ating signal in thesense that substantially all' ripple be taken out of the rectifiedcurrent.v and the voltage applied to the plates of the cathode ray tubebe smooth.

To improve the sensitivity of the temperature ing signal is impressedupon split secondary windings Al and 42, arranged in such manner thattubes 43 and 44 will conduct or be cut off simultaneously. Resistor 45isused to. balance the two tubes','and load resistor 45 provides for thevoltage drop to be amplified,'rectified and displayed on the cathode raytube screen.

In operation, assuming first no signal from the thermocouple, asinusoidal wave of 500 cycles per second, for example, is impressed uponthe primary Winding'All and is thus introduced through split windings 4|and 42 to tubes Q3 and 44.

. 'Ihesewindings are arranged so that, on the positive half -cyc le-' ofthe sinusoidal wave, both tubes indication, a thermocouple biasingcircuit comprising a cell l9, resistor 20, and adjustable re sistor 2!is provided in order to make it possible during a single heating cycleof the instrument to have the cathode ray tube beam swing across thescreen and back, as the temperature indication. This device providesdoubly sensitive: temperature indication in terms of degrees per inch ofdeflection of the beam. In settin this auxiliary thermocouple biasingcircuit, cell ii) is oriented to give a potential ofpolarity opposite tothat which will be generated by the heating of the thermocouple and ofabout one half the main imum. value expected. Thus, during the heatingof a specimen, there is, at first, a gradual diminution of the amplitudeof the voltage pulses to zero, followed by a. gradual enlargement ofpulse amplitude with the pulses. offset from. the first by one-halfcycle. lhe result is a reversal in the direction of the deflection" ofthe beam during. a single heating cycle. The positioning controls of thecathode ray oscillograph and the amplifier can be used to start thetrace on. one. side of the screen and to amplify the deflecting voltageso that reversal of the trace will occur at the opposite side of thescreen. The circuits associated with said controls are not shown forthey are conventional and form no part of. our invention.

Figure 2 illustrates an alternative method and apparatus. for deriving.the pulsating signal from the thermoelectric voltage. It is seen thatthe contacts ll of Figure l hav been replaced by a switch. tube 22, thethermocouple voltage being applied to one grid and a periodic signalbeing applied to another grid. The amplitude andfrequency of theperiodic signal can be so adjusted that the tube will be periodicallyconducting and cut off. Variation of the time the tube. is out oh andthe frequency of the cut-offperiods is controlled by th amplitude andfrequency of the periodic signal. This signal can be a-sinusoidal,square, or sawtooth wave.

Figure 3 illustrates. a second alternative method and apparatus forderiving the pulsating signal and takes the form of a relay 3D activatedby a periodic signal generator. This signal can .be a sinusoidal,square, or sawtooth wave, and the re lay can be built to operate, oropen, at a given voltage. By varying the length of the signal period orits amplitude, the pulse repetition frequency of the thermoelectricsignal sent to the amplifier and cathode ray tube can be'varied asdesired.

Figure 4 illustrates a third alternative method and apparatus forderiving the pulsating signal in the form of a device which, for manypurposes, may be preferable to those of Figures 2 and 3. This deviceconsists of a transformer having a primary winding 40. through which analternatwill conduct, and, on the negative half-cycle, both tubes-willbe cut ofi. The impressed signal is of such amplitude as to effectcomplete cut-ofi and complete saturation'conduction of the tubes.

When both tubes are conducting it appears that the tubes as shown in thediagram will conduct in such manner as to produce. opposite currents inload resistor (5 3. Because of inherent physical dilficultiesencountered in matching tubes to draw identical currents, the variableresistor 45 is used to effect the match. Under conditions of optimummatching, there is, therefore, no current flow through load resistor 46.

When. the thermocouple I0 is heated, for example, to such a temperatureas to produce a thermo-electromotive force of a few millivolts, on thenegative half cycle of the signal impressed through winding 48, therewill be no current flow through the tubes 43 and 44 and therefore no.voltage drop across load resistor 45. On the positive half cycle,however, tubes 43 and 44 will conduct and, under conditions of optimummatching of these tubes, only the current suplied by the. thermocouplewill produce a voltage drop across th load resistor 45. A pulsatingsignal, whose amplitude is substantially that of the thermoelectricvoltage, is thus produced at the desired frequency.

In order toobtain a photographic record of aspecific temperature cycle,a time reference plot of temperature change is used. Inasmuch as we havedescribed the device wherein temperature is plotted by the verticaldeflection of the cathode ray beam, the time reference will, of course,be plotted by the horizontal deflection of the oathode ray beam. This iseasily accomplished by applying a linear sawtooth wave of desiredfrequency from a sawtooth wave generator to the horizontal deflectionplates of the cathode ray tube.

It is understood that, although we have described our invention throughan illustration whereby temperature potential is applied to the verticaldeflection plates to form the ordinate and time is plotted as theabscissa, these factors may just as readily be presented as abscissa andordinate respectively.

' It is to be understood that our invention is not restricted to thepresent disclosure to any extent otherwise than as restricted by themanher in which such invention is claimed.

The invention described herein may be manufactured and used by or for thGovernment of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What we claim is:

' 1. A temperature variation indicating apparatus comprising, incombination, a temperature detecting circuit including a thermoelectricelement, a potential source for biasing said thermoelectric element at apredetermined level equal to substantially half the maximumthermoelectrio output voltage for a given temperature variation, aninterrupter in said thermoelectric circuit for periodically making andbreaking said circuit to derive a pulsating signal therefrom, anamplifier for amplifying said pulsating signal, a cathode ray tube, anda pair of rectifier elements driven by the output of said amplifier andconnected to said cathode ray tube to couple signals having oppositepolarity to opposite deflection plates of said cathode ray tube.

2. In a temperature variation indicating appa= ratus, a thermoelectricelement for producing an output voltage responsive to temperature, abiasing potential source connected in serie with said thermoelectricelement for biasing said element at a predetermined level equal tosubstantially half its maximum output voltage for a given temperaturevariation, means for deriving a pulsating signal from said outputvoltage comprising, first and second tubes each having at least cathode,anode, and control grid electrodes, a transformer having primary andfirst and second secondary windings, an alternating voltage sourcealternating at the desired pulsing rate and connected to said primary,said first and second secondaries being connected respectively betweenthe cathode and grid electrodes of said first and second tubes, saidlast named connection being made with like polarity to drive said gridsin phase, a load resistor, first and second interconnecting meansrespectively connecting the cathode of said first tube to the anode ofsaid second tube and the cathode of saidsecond tub to the anode of saidfirst tube, said load resistor, thermoelectric element and biasing meansbeing connected in series between said first and second interconnectingmeans, an amplifier hav ing its input connected across said loadresistor, a cathode ray tube, and a pair of rectifier elements driven bythe output of said amplifier and connected to said cathode ray tube tocouple signals having opposite polarity to opposite deflection plates ofsaid cathode ray tube.

3. In a temperature variation indicating apparatus, a thermoelectricelement for producing an output voltage responsive to temperature, abias= ing potential source connected in series with said thermoelectricelement for biasing said element at a predetermined level equal tosubstantially half its maximum output voltage for a given temperaturevariation, means for deriving a pulsating signal from said outputvoltage com-= prising, first and second tubes each having at leastcathode, anode, and control grid electrodes, a transformer havingprimary and first and second secondary windings, an alternating voltagesource alternating at the desired pulsing rate and connected to saidprimary, said first and second secondaries being connected respectivelybetween the cathode and grid electrodes of said first and second tubes,said last named connection being made with like polarity to drive saidgrids in phase, a load resistor, first and second interconnecting meansrespectively connecting the oathode of said first tube to the anode ofsaid second tube and the cathode of'said second tube to the anode ofsaid first tube, said load resistor, ther= moelectric element andbiasing means being con nected in series between said first and secondinterconnecting means.

ARTHUR L. CHRISTENSON. CLARENCE E. JACKSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,363,267 Porter Dec. 28, 19201,753,486 Travis Apr. 8, 1930 2,113,164 Williams Apr. 5, 1938 2,166,310Lord July 18, 1939 2,178,471 De Bruin Oct. 31, 1939 2,293,135 HallmarkAug. 18, 1942

